Aqueous silsesquioxane dispersions having low concentrations of reaction byproducts

ABSTRACT

Methods of making a composition are disclosed, which comprises: i) forming a dispersion of particles comprising: a) silica, b) a non-volatile cation, and c) water, wherein the non-volatile cation is not ammonium; ii) adding at least one organosilyl coupling agent of formula R 1 —(R 2 —O) 3 —Si where R 1  is selected from the group consisting of a substituted alkyl and unsubstituted alkyl, and R 2  is selected from the group consisting of methyl, ethyl, propyl and butyl, wherein the substituted alkyl of R 1  is not aminoalkyl; iii) reacting the organosilyl coupling agent with the dispersion of particles to form a mixture comprising a silsesquioxane and an alcohol; and iv) removing the alcohol from the mixture by vacuum distillation, wherein final concentration of the alcohol is about 1% by weight or less of the total mixture. Further disclosed are compositions comprising an aqueous dispersion comprising silsesquioxane, a non-volatile cation and an alcohol, and methods of using the composition.

CROSS-REFERANCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.12/722,264, filed Mar. 11, 2010, now U.S. Pat. No. 8,420,734, whichclaims benefit of priority from U.S. Provisional Application No.61/159,825, filed Mar. 13, 2009.

FIELD OF THE INVENTION

The present invention relates to a silsesquioxane dispersion havingdistinctively low concentrations of volatile alcohol reaction byproductssuitable for application to carpets and other textiles.

BACKGROUND OF THE INVENTION

Silsesquioxane dispersions have been found to be useful for treatment ofcarpets and textiles in concert with fluorochemical resins to impart oiland water repellency and general resistance to soil as disclosed in U.S.Pat. No. 6,225,403 (Knowlton). However, where such dispersions areproduced by condensation reactions using alkyltrialkoxysilanes,unacceptably large amounts of alkoxy compounds (for example methanol inthe case of alkyltrimethoxysilanes) may be present as a byproduct of thesilane reaction. Alkoxy compounds such as methanol are generallyundesirable in treatment compositions and on treated articles but cannotbe removed effectively during the condensation reaction process sincethe silanes are sufficiently volatile that a removal process is likelyto remove the desired reactant as well. Upon completion of the reaction,the usual methods of cleaning and re-dispersing the silsesquioxaneparticles are cumbersome and are likely to result in extensive andundesirable agglomeration of the reaction products and consequent lossof both effectiveness and yield.

Surface-modified silica dispersions that have been produced bycondensation reactions with alternative reagents result in alternativebyproducts which are also undesirable, examples being triethoxysilanesyielding ethanol, and halogenated silanes yielding halogen acids.Halogen acids can cause undesirable agglomeration owing to relatedchanges in pH, while ethanol is undesirable for articles such as carpetbecause, like methanol, it is a volatile organic compound.

Several methods are potentially useful to remove the above mentionedalcohol reaction byproducts from water. However, it has been found thatmany are unsuitable when applied to silsesquioxane dispersions of thekind applicable to carpets and textiles. In particular, it has beenfound that undesirable agglomeration of silsesquioxane dispersionsresults when evaporation is employed to remove either methanol orethanol from such systems. Dispersions that are particularly applicableto carpets and textiles have typically been formed in aqueous systemsbuffered with ammonium counter-ions to stabilize them. Theammonium-ammonia equilibrium may be adversely affected by evaporation,so that the resulting system may no longer support the dispersion of allof the particles, and precipitation of some or all of the suspendedparticles of the dispersion may ensue. It has also been observed thatsilsesquioxane dispersions built from silica cores suffer from the sameissues that are encountered with the surface-modified silicadispersions.

U.S. patent application number 2008/0216709A1 (Steingrover) teaches thatacidic aminoalkylsilane modified silica particles are stable in acidicaqueous solutions in contrast to other alkylsilane materials. However,the organic amine functionality disclosed by Steingrover is not capableof creating hydrophobic, soil resistant and oil repellent fabrics.

SUMMARY OF THE INVENTION

Therefore, there is a need for an efficient and effective route toremove dissolved byproducts as described above from silsesquioxanedispersions while maintaining the stability of the dispersion.

In accordance with the present invention, changes to the method offormation of certain silsesquioxane dispersions allow efficient andeffective removal of dissolved byproducts in the silsesquioxanedispersions while maintaining the stability of the dispersion.Specifically, a generally hydrophobic silsesquioxane dispersion thatincludes a non-volatile free cation is stable to vacuum distillation.Sodium stabilized surface-modified silica particles or silica-coresilsesquioxanes, for example, tolerate vacuum distillation of byproductslike methanol to a very low level, the level determined by a combinationof vacuum level, temperature, stirring, and time.

In one aspect, a method of making a composition is disclosed, whichcomprises: i) forming a dispersion of particles comprising: a) silica,b) a non-volatile cation, and c) water, wherein the non-volatile cationis not ammonium; ii) adding at least one organosilyl coupling agent offormula R₁—(R₂—O)₃—Si where R₁ is selected from the group consisting ofa substituted alkyl and unsubstituted alkyl, and R₂ is selected from thegroup consisting of methyl, ethyl, propyl and butyl, wherein thesubstituted alkyl of R₁ is not aminoalkyl; reacting the organosilylcoupling agent with the dispersion of particles to form a mixturecomprising a silsesquioxane and an alcohol; and iv) removing the alcoholfrom the mixture by vacuum distillation, wherein final concentration ofthe alcohol is about 1% by weight or less of the total mixture. Thepresent invention further relates to a composition comprising asilsesquioxane, a non-volatile cation and an alcohol, and methods ofusing the composition.

In another aspect, a composition is disclosed, which comprises anaqueous dispersion comprising a silsesquioxane, a non-volatile cationand an alcohol, wherein the concentration of alcohol is about 0.5% byweight or less of the total composition and wherein the non-volatilecation is not ammonium.

In a further aspect, a method of treating carpet is disclosed, whichcomprises applying a composition comprising an aqueous dispersioncomprising a silsesquioxane, a non-volatile cation and an alcohol,wherein the concentration of alcohol is about 0.5% by weight or less ofthe total composition and wherein the non-volatile cation is notammonium to the carpet and drying the carpet.

DETAILED DESCRIPTION OF THE INVENTION

Disclosed is a method of making a composition comprising: i) forming adispersion of particles comprising: a) silica, b) a non-volatile cation,and c) water, wherein the non-volatile cation is not ammonium; ii)adding at least one organosilyl coupling agent of formula R₁—(R₂—O)₃—Siwhere R₁ is selected from the group consisting of a substituted alkyland unsubstituted alkyl, and R₂ is selected from the group consisting ofmethyl, ethyl, propyl and butyl, wherein the substituted alkyl of R₁ isnot aminoalkyl; iii) reacting the organosilyl coupling agent with thedispersion of particles to form a mixture comprising a silsesquioxaneand an alcohol; and iv) removing the alcohol from the mixture by vacuumdistillation, wherein final concentration of the alcohol is about 1% byweight or less of the total mixture. Optionally, the final concentrationof the alcohol can be about 0.5% by weight or less of the total mixture,including about 1000 ppm or less of the total mixture. The dispersioncan also be referred to as a sol. The composition made by this methodcan be used in fabric treatment, including treating carpets

A combination of temperature and pressure is used for vacuumdistillation to remove the alcohol. The temperature can be between fromabout 30° C. and about 80° C., including from about 40° C. to about 60°C., and from about 40° C. to about 50° C. The distillation temperaturecan also be about 40° C. and about 45° C. The vacuum applied duringdistillation is less than 200 torr, including less than 150 ton, lessthan 100 torr, less than 75 torr, and about 50 torr. The vacuum appliedcan also be in the range from about 75 torr to about 50 torr, includingabout 75 torr. One combination of temperature and pressure to remove thealcohol is about 45° C. and about 75 ton.

The non-volatile cation can be selected from alkaline metals, forexample the group consisting of lithium, sodium, potassium, and cesium.Divalent non-volatile cations, for example magnesium and calcium, can beemployed in the process of the present invention but they may have apropensity to interact (form precipitates) with other chemicalssubsequently added or combined with the resultant composition. Thenon-volatile cation of the present invention is not ammonium. R₂ can beselected from the group consisting of methyl, ethyl and propyl. R₁ canbe selected from the group consisting of methyl, ethyl, propyl andbutyl, or R₁ can be a haloalkyl. The substituted alkyl of R₁ is notaminoalkyl.

The disclosed method can further comprise v) mixing the product producedin step iv) with an aqueous dispersion comprising a fluorochemicalresin. Additionally, the disclosed method can further comprise vi)applying the product of step v) to a carpet or fabric.

Also disclosed is a composition comprising a silsesquioxane, anon-volatile cation and an alcohol, wherein the concentration of alcoholis about 1% by weight or less of the total composition and wherein thenon-volatile cation is not ammonium. The concentration of alcohol can beabout 0.5% by weight or less of the total composition, including about1000 ppm or less of the total composition. The composition can furthercomprise a fluorochemical resin; and optionally a carpet or fabricwherein the concentration of alcohol is about 100 ppm or less of thetotal carpet or fabric weight, including about 10 ppm or less of totalcarpet or fabric weight.

Further disclosed is a method of treating a carpet comprising, applyingthe above composition to the carpet and drying the carpet. The treatedcarpet can comprise an alcohol concentration of about 10 ppm or less oftotal carpet weight.

The disclosed method creates a silsesquioxane, surface-modified silica,and silica-core silsesquioxane particles as well as other materials withreactive silicon-based chemical groups made or modified using reactivesilanes of the general formula R₁—(R₂—O)₃—Si where R₁ carries thedesired surface chemistry functionality of the final particles ormaterial and can be a substituted or unsubstituted alkyl chain, monomer,or polymer, and R₂ is a short-chain alkyl group (R₂ is generally thesame for all three oxygen-containing pendant groups represented here,but may be different). The result of the reactions of interest is theliberation of R₂—OH into the medium. The medium can also contain one ormore agents to effect a stable dispersion of the original particles (inthe case in which silica or other particles are used as the startingmaterial) or to support the formation and dispersion of the particlesbeing formed.

One method to create aqueous particle dispersions is to combine chargedparticles with counter-ions. Anionically-charged particles are suitablein cases where attraction to a cationically charged substrate is desiredor where dictated by the charge of other particles or chemicals in asolution.

For products that are to be used in aqueous media, water can be asuitable reaction medium. This avoids removal of undesired solvents,recovery of reaction products, and subsequent dispersion of therecovered products into water. In the case where the desired product isan aqueous dispersion of micro-and nanoparticles, creation of suchparticles in non-aqueous media with separation from the reaction solventand subsequent dispersion in water without agglomeration orprecipitation can be especially difficult without the addition ofsurfactants. Unfortunately, such surfactants compromise the efficacy ofproducts to make carpets and textiles more hydrophobic and soilresistant.

Therefore, when water is used in reactions between silicates andorganosilanes, the byproduct alcohol (methanol, ethanol, etc.) becomesdispersed in water. With the presence of the byproduct alcohol (andpossibly other low-molecular weight impurities) volatile organic carbon(VOC) content may limit the ultimate usage of the final article orproduct.

As described above, creation of a dry powder and re-dispersion in watercan be an available route that would result in the elimination of theVOC content, but agglomeration, precipitation, and cost are obstacles.Vacuum distillation can be used to remove volatile contaminants fromsolutions or dispersions from the mixture. However, some byproducts orimpurities have an affinity for the medium that limits the amount whichcan be removed, such as when an azeotrope is formed.

Ammonium has been conventionally used as a counter-ion for anionicallycharged particles as it is compatible with many formulations andapplications, and it provides some control of pH. It has been observedthat application of the vacuum distillation method, with or withoutheating and/or stirring, fails when used with ammonium-stabilizedsilsesquioxane particle systems that are not otherwise supported, forexample, by surfactants or other stable dispersing agents. For manyapplications, however, the additional material of such stabilizingagents is deemed undesirable. Among such applications, practicalexamples include the silsesquioxane particle systems appropriate toanti-soiling formulations for carpet, because the stabilizing agentstend to be chemically compatible with water, oil and dirt.

In one aspect of the disclosed method, the problem of byproduct alcoholcontamination in silsesquioxane dispersions has been solved by using anon-volatile counter-ion (not ammonium) to stabilize the aqueousdispersion while methanol is removed through a process of vacuumdistillation. In the case of the anionic silsesquioxane particlesdescribed above, the ammonium counter-ions can be replaced with sodiumcounter-ions. Since sodium ions are retained during vacuum distillation,the charge-stabilized dispersion is not disrupted and the dispersionremains stable throughout the process and in subsequent storage. Othercounter-ions can include lithium, potassium, cesium, magnesium andcalcium.

Methanol is effectively and efficiently removed even from relativelyunstable hydrophobic silsesquioxane dispersions by applying vacuumdistillation with mild heating. Under similar conditions, a largefraction of ethanol or propanol can be removed if ethoxy or propoxysilanes were used as reactants. Other relatively volatile byproducts canalso be removed at the same time. The extent to which the byproducts andother volatiles are removed is dependent upon the specific conditionsutilized (temperature, vacuum, and time). In all cases, the result is astable dispersion with a substantially reduced concentration of volatileorganic compounds remaining.

Methods are described where methanol is reduced from an initialconcentration level of over 1% by weight to as little as 100 ppm or lessin a single step process.

It is to be understood that various combinations of temperature,stirring, vacuum level, and time can be employed to enable thedistillation of methanol or other alcoholic byproducts from reactionmixtures which may initially contain various concentrations of suchalcohol, from as little as 0.1% to as much as 10% or more by weight, toachieve a desired resultant concentration. Depending on the intendeduse, residual methanol concentration may be reduced to less than about10,000 ppm, or may be reduced to even less than 100 ppm. Levels as lowas 20 ppm are achievable by further adjusting the conditions (highertemperature, improved vacuum, and/or longer time). Also disclosed is asodium stabilized dispersion of alkylsilated silica which containsapproximately 0.9% to 5% methanol that can be reduced to about 500 ppmmethanol, including less than about 150 ppm methanol.

EXAMPLES

Test Methods

The amount of alcohol byproduct present in the aqueous dispersion beforeand after the vacuum distillation process was determined using gaschromatography with mass spectral detection (GC-MS). The residualalcohol in the dispersion was preferentially removed by extraction withethyl acetate. The extract was filtered to remove particulates and therelative concentration of methanol was determined by GC-MS in comparisonwith known standards by the conventional method of standard additions.

Comparative Example 1

Approximately 1.2 kg of Ludox AS-40, from GraceDavidson, described as anammonium stabilized suspension of silica particles in water that isapproximately 40% by weight silica, with an average particle diameter ofabout 20 to 30 nm and a nominal pH of 9, was placed in a 20-Literreactor. The particle suspension was slowly reacted with 30 g ofmethyltrimethoxysilane at about 30° C., to create an aqueous suspensionof alkylsilane modified particles, which can be called silica-coresilsesquioxanes, having a concentration of about 1% by weight ofmethanol. Slow stirring was maintained at about 40° C. and vacuum wasapplied to achieve about 50 torr pressure for about four hours togradually remove the methanol. Significant precipitation solids werefound, indicating agglomeration of particles and initiation of thebreakdown of the stable particle dispersion.

Example 2

Approximately 1.2 kg of Ludox TM-40, from GraceDavidson, described as asodium stabilized suspension of silica particles in water that isapproximately 40% by weight silica, with an average particle diameter ofabout 20 to 30 nm and a nominal pH of 9, was placed in a 20-Literreactor. The particle suspension was slowly reacted with 30 g ofmethyltrimethoxysilane at about 30° C., to create an aqueous suspensionof alkylsilane modified particles, called silica-core silsesquioxanes,having a concentration of about 1% by weight of methanol. Slow stirringwas maintained at about 40° C. and 50 ton pressure, gradually removingthe methanol. After about 10 hours, less than 100 ppm of methanol wasfound to remain in solution. Little agglomeration of particles wasobserved.

While the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives,modifications, and variations will be apparent to those skilled in theart in light of the foregoing description. Accordingly, it is intendedto embrace all such alternatives, modifications, and variations as fallwithin the spirit and broad scope of the appended claims.

What is claimed is:
 1. A composition consisting essentially of a) anaqueous dispersion consisting essentially of a silsesquioxane, anon-volatile cation and an alcohol, wherein the concentration of alcoholis about 0.5% by weight or less of the total composition and wherein thenon-volatile cation is not ammonium, and b) a fluorochemical resin. 2.The composition of claim 1 wherein the concentration of alcohol is bout1000 ppm by weight or less of the total composition.
 3. The compositionof claim 1 wherein the concentration of alcohol is about 200 ppm or lessof the total composition.
 4. A method of treating a carpet comprisingapplying the composition of any one of claim 1-3 to the carpet anddrying the carpet.
 5. A carpet produced by the method of claim 4,comprising an alcohol concentration of about 0.1 ppm or less of totalcarpet weight.